The doctors at a hospital in Volgograd, about 550 miles southeast of Moscow, had participated in the tests for pediatric vaccines called Varilrix and Priorix Tetra beginning in late 2005, the prosecutor general's office said in a statement posted on its Web site.

A total of 112 children between the ages of one and two were involved in the trials, prosecutors said. Officials opened their inquiry when a parent complained to prosecutors after her daughter suffered medical complications, apparently from the vaccine.

Parents were allegedly told by the doctors that the vaccines were routine rather than experimental, prosecutors said.